[IRCA] Longwire for Tecsun PL-360

[Lostgallifreyan <z.crow@xxxxxxxxxxxxxx>]

Hello. I just signed up and already answered a message, but might do well to stick to a question, I'm not informed enough to give many answers...

I already made a longwire modification for a PL-390, about 9o turns on the internal ferrite rod at the free end, wired between ground and the unused 'ring' connector on the antenna socket. This works well, but apparently someone did better with as few as siz turns, closer to the main winding, I'll have to try that on the next one I modify. :)

The PL-360 is a different matter. It has a (very cute) tiny internal ferrite, which gets cut out when plugging in the external supplied ferrite rod antenna. I've tried small loops of 10 to 20 turns, about an inch diameter, one close to the internal ferrite, with good(ish) results, better was around the external ferrite, by as much as 9dB more. I intend to mount it in an external case for better physical endurance, a full size phone jack, BNC antenna socket and such, and for the fastest way to set things up when ready, I aim to have one longwire serve all bands, using one socket to connect it. (possibly with a switch to select internally between SW/VHF and AM).

To my question... Can I get good results using a small ferrite toroid (about an inch, permeability allegedly around 5000 to 5000) to satisfy the PL-360's need for about 350µH of inductance to tune on AM while dramatically reducing local EMI leaking into the doings?

The idea seems good in concept, but I have trouble with it so far. I calculated (using three online sources to check with first) that 11 turns spaced around most of the toroid should get the required inductance on this core. I wound a bifilar winding, 1:1, so the other one got the longwire to ground. I found that selectivity was almost as poor as if I tried plugging the wire straignt to the socket leaving the radio with no inductance fit to tune with. :) This happened whether I commoned the two ground ends or not. I'm fairly sure the wire didn't get scraped and shorted though the ferrite, so I don't think that's why...

My next move is to try to measure the inductance by a half-volt method for calulation with a method I researched yesterday, to see if I'm getting a wildly wrong result out of that toroid, but I also think askign here is a good idea.

Crow.

PS. I discovered Gary DeBock's big external ferrite on a PL-390, and it's a very cool idea too, but before I found that, I'd tried a cheap headphone cable cable extension and tried the supplied antenna through it. It worked fine, through a length of over 7 feet, and it turns out that the cable has an odd construction, red to ring, white to tip, reversing convention, and only the red is shielded! Meaning, that the white one used in this case had no shield. Despite this, the results were good, so I'm wondering if building a system to mount on a PL-360 is needed at all, it looks like a convenient remote antenna might be just as feasible, and less likely to stress a fragile radio. I have no idea how long a cable we might get away with though. The reason I'm considering all this is that my external antenna might eventually better be a loop than a longwire, as good SNR as ever makes a batter result, especially given the weird AGC in a Tecsun radio.

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